The present invention pertains to viscous liquid applying apparatus useful in applying a wide variety of liquid adhesives to web, sheet materials, or other surfaces. The apparatus and related method are particularly useful in the manufacture of corrugated paperboard products.
Roll-type applicators have long been used to apply adhesives to the face of a running web or similar sheet materials. In the manufacture of corrugated paperboard, for example, two or more glue machines are typically used in a corrugator. Each single facer in a corrugator includes a glue machine to apply the adhesive, commonly a starch-based glue, to the flute tips of a corrugated medium web prior to being joined with a liner web in the single facer. Further downstream, a similar glue machine is utilized to apply adhesive to the exposed flute tips on the single face web prior to its joinder with the other liner web in a double backer. Multi-wall board manufacture requires an additional single facer glue machine and a double backer glue machine for each additional single face web.
Roll-type adhesive applicators for single face and double face corrugated webs have typically utilized multi-roll constructions. U.S. Pat. Nos. 3,053,309, 3,671,361 and 4,369,080 are typical of one multi-roll construction in which a glue roll is partially immersed in a reservoir through which it rotates to pick up a layer of glue on its surface, which layer is metered to a desired thickness by engagement with a rotating doctor roll. The glue roll continues to rotate into contact with the flute tips of the corrugated medium. The corrugated medium may either be supported on the toothed roll of corrugator in a single facet or against a backing roll in contact with the liner face of a single face web in a double backer.
Another type of multi-roll glue applicator is shown in U.S. Pat. No. 2,979,661. In this patent a glue roll, operating as previously described, carries the initial glue layer onto the surface of a counterrotating transfer roll which, in turn, carries the transferred layer onto the exposed corrugated medium flute tips. Thus, the glue roll itself also provides the doctor roll function in transferring a metered layer of the glue to the transfer roll. Two-roll metering systems, when handling more viscous materials and traveling at higher speeds, are subject to spreading apart or even bowing as a result of the highly viscous adhesive or other material being forced into the space between the counterrotating rolls. As a result and as speed increases, more adhesive than desired remains on the glue roll and the layer may be very uneven.
U.S. Pat. Nos. 3,300,359 and 4,806,183 show glue or adhesive applicators in which a single glue roll picks up adhesive from a reservoir, is contacted by a smooth-edged doctor blade to meter the amount of adhesive remaining on the roll and transfers the glue to the flute tips of a corrugated medium or single face corrugated web. However, the glue rolls are constructed with a recessed cellular surface forming pockets for the glue, in the manner of an anilox roll used in printing and roll coating. The doctor blades wipe the cylindrical outer surfaces of the rolls to remove essentially all of the adhesive, except for the amounts retained in the cells. Smooth-edged doctor blades are also used to apply a metered layer of adhesive to the surface of a smooth glue roll in a similar manner. All of the foregoing doctor blades are typically forward acting or disposed with the plane of the blade oriented in the direction of roll movement. All of these types of metering systems are subject to a similar problem as that identified with respect to the roll metering systems described above. Again, when applying relatively viscous adhesive materials with a forward running doctor blade, the hydraulic force of the liquid tends to separate the blade from the roll, particularly as speeds increase. As a result, the blade will lift off the roll by a distance greater than desired, resulting in loss of control of the metered layer of adhesive being applied.
U.S. Pat. No. 3,972,763 discloses a glue applicator for either a single facer or a double backer in which a helically grooved glue roll has adhesive applied to the surface thereof by a chambered doctor blade which engages the crest of the helical land, leaving the adhesive in the adjacent helical recess. The adhesive is transferred directly from helically grooved roll to the flute tips of the web. In another disclosed embodiment, the glue roll has a smooth cylindrical surface and the adhesive is applied to the surface of the roll in laterally spaced wavy bead lines created by a roll-contacting oscillating grooved metering roll or notched metering blade. In all embodiments, the helical or beaded pattern of the adhesive on the glue roll is applied directly to the flute tips such that each flute receives laterally spaced dots of adhesive. The dots are spread by subsequent contact with the liner web joined to the fluted medium. The apparatus is adapted particularly to utilize hot melt adhesives in place of conventional starch based adhesives.
The prior art is thus characterized by glue machines which utilize complex multi-roll arrangements, intricate applicator or glue roll surface constructions, or other complex applicator mechanisms. All of the foregoing metering devices are subject to loss of metering control with viscous materials and higher operating speeds. It would be desirable, therefore, to provide a simple but effective assembly for applying a liquid adhesive to a moving web, sheet of material, or other surface.